Fluoride was added to the water supplies of public schools in three Virginia counties to study the anti-caries effectiveness of fluoride ingestion: throughout grades K-6 (Cumberland Co.); throughout grades K-8 (Matthews Co.); and throughout grades K-12 (Amelia Co.). All school populations live in areas that have no central water supplies and where the drinking waters contain negligible concentrations of fluoride. In May, 1979, baseline dental examinations (DMFS Index) were made of a total of approximately 4,200 students in grades K-12 in the three counties. In December 1979, schools containing the required grade levels for study fluoridated at a concentration of 4.5 times that recommended for community fluoridation in the geographic area. Follow-up examinations will be conducted after 3, 7, 9 and 13 years of study as increasingly more subjects become continuously exposed to fluoridated water at school for the desired periods of time.